Run Webpack Watch From Node.js

May 23, 2019

If you have a Node.js server that serves content using express-static and you compile your content with Webpack, you don't have to run both npm run dev and webpack --watch. Your npm run dev script can run webpack --watch for you, no CLI required, using Webpack's Node API.

Here's an example of importing Webpack in a Node.js script and watching a file for changes.

const webpack = require('webpack');

// Defining the webpack config inline, but you can replace this
// with `require('./webpack.config.js')`
const config = {
  mode: 'development',
  entry: `${__dirname}/example/app.js`,
  output: {
    path: `${__dirname}/example`,
    filename: 'app.min.js'
  }
};
const compiler = webpack(config);
const watcher = compiler.watch({}, function(err) {
  // Gets called every time Webpack finishes recompiling.
});

fs.writeFileSync(`${__dirname}/example/app.js`,
  'module.exports = \'Hello, World\';');

Because of Node.js' event loop, you don't explicitly have to create new threads. Your Node process can be both an HTTP server and a Webpack compiler. Here's an example of a Node.js script:

const app = require('express')();
const webpack = require('webpack');

app.use(require('express-static')(`${__dirname}/example`));
const server = await app.listen(3000);

const config = {
  mode: 'development',
  entry: `${__dirname}/example/app.js`,
  output: {
    path: `${__dirname}/example`,
    filename: 'app.min.js'
  }
};
const compiler = webpack(config);
const watcher = compiler.watch({}, function(err) {
  // Gets called every time Webpack finishes recompiling.
});

fs.writeFileSync(`${__dirname}/example/app.js`,
  'module.exports = \'Hello, World\';');

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